221 lines
5.9 KiB
Groff
221 lines
5.9 KiB
Groff
.\" Copyright (c) 1990, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)mpool.3 8.1 (Berkeley) 6/4/93
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.\" $FreeBSD$
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.\"
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.TH MPOOL 3 "June 4, 1993"
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.UC 7
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.SH NAME
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mpool \- shared memory buffer pool
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.SH SYNOPSIS
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.nf
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.ft B
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#include <db.h>
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#include <mpool.h>
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MPOOL *
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mpool_open (DBT *key, int fd, pgno_t pagesize, pgno_t maxcache);
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void
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mpool_filter (MPOOL *mp, void (*pgin)(void *, pgno_t, void *),
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.ti +5
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void (*pgout)(void *, pgno_t, void *), void *pgcookie);
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void *
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mpool_new (MPOOL *mp, pgno_t *pgnoaddr);
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void *
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mpool_get (MPOOL *mp, pgno_t pgno, u_int flags);
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int
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mpool_put (MPOOL *mp, void *pgaddr, u_int flags);
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int
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mpool_sync (MPOOL *mp);
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int
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mpool_close (MPOOL *mp);
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.ft R
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.fi
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.SH DESCRIPTION
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.IR Mpool
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is the library interface intended to provide page oriented buffer management
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of files.
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The buffers may be shared between processes.
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.PP
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The function
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.I mpool_open
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initializes a memory pool.
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The
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.I key
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argument is the byte string used to negotiate between multiple
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processes wishing to share buffers.
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If the file buffers are mapped in shared memory, all processes using
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the same key will share the buffers.
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If
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.I key
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is NULL, the buffers are mapped into private memory.
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The
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.I fd
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argument is a file descriptor for the underlying file, which must be seekable.
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If
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.I key
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is non-NULL and matches a file already being mapped, the
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.I fd
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argument is ignored.
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.PP
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The
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.I pagesize
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argument is the size, in bytes, of the pages into which the file is broken up.
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The
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.I maxcache
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argument is the maximum number of pages from the underlying file to cache
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at any one time.
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This value is not relative to the number of processes which share a file's
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buffers, but will be the largest value specified by any of the processes
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sharing the file.
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.PP
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The
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.I mpool_filter
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function is intended to make transparent input and output processing of the
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pages possible.
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If the
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.I pgin
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function is specified, it is called each time a buffer is read into the memory
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pool from the backing file.
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If the
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.I pgout
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function is specified, it is called each time a buffer is written into the
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backing file.
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Both functions are called with the
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.I pgcookie
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pointer, the page number and a pointer to the page to being read or written.
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.PP
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The function
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.I mpool_new
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takes an MPOOL pointer and an address as arguments.
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If a new page can be allocated, a pointer to the page is returned and
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the page number is stored into the
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.I pgnoaddr
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address.
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Otherwise, NULL is returned and errno is set.
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.PP
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The function
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.I mpool_get
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takes a MPOOL pointer and a page number as arguments.
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If the page exists, a pointer to the page is returned.
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Otherwise, NULL is returned and errno is set.
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The flags parameter is not currently used.
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.PP
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The function
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.I mpool_put
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unpins the page referenced by
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.IR pgaddr .
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.I Pgaddr
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must be an address previously returned by
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.I mpool_get
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or
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.IR mpool_new .
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The flag value is specified by
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.IR or 'ing
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any of the following values:
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.TP
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MPOOL_DIRTY
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The page has been modified and needs to be written to the backing file.
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.PP
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.I Mpool_put
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returns 0 on success and -1 if an error occurs.
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.PP
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The function
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.I mpool_sync
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writes all modified pages associated with the MPOOL pointer to the
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backing file.
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.I Mpool_sync
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returns 0 on success and -1 if an error occurs.
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.PP
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The
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.I mpool_close
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function free's up any allocated memory associated with the memory pool
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cookie.
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Modified pages are
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.B not
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written to the backing file.
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.I Mpool_close
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returns 0 on success and -1 if an error occurs.
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.SH ERRORS
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The
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.I mpool_open
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function may fail and set
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.I errno
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for any of the errors specified for the library routine
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.IR malloc (3).
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.PP
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The
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.I mpool_get
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function may fail and set
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.I errno
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for the following:
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.TP 15
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[EINVAL]
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The requested record doesn't exist.
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.PP
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The
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.I mpool_new
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and
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.I mpool_get
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functions may fail and set
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.I errno
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for any of the errors specified for the library routines
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.IR read (2) ,
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.IR write (2) ,
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and
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.IR malloc (3).
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.PP
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The
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.I mpool_sync
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function may fail and set
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.I errno
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for any of the errors specified for the library routine
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.IR write (2).
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.PP
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The
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.I mpool_close
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function may fail and set
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.I errno
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for any of the errors specified for the library routine
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.IR free (3).
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.SH "SEE ALSO"
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.IR dbopen (3),
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.IR btree (3),
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.IR hash (3),
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.IR recno (3)
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